This invention relates to herbicidal compositions, and wore particularly relates to herbicidal compositions containing N-phosphonomethylglycine, a quaternary ammonium compound and propylene glycol or polypropylene glycol.
N-Phosphonomethylglycine, known in the agricultural chemical art as glyphosate, is a highly effective and commercially important phytotoxicant useful in controlling the growth of germinating seeds, emerging seedlings, maturing and established woody and herbaceous vegetation, and aquatic plants. N-phosphonomethylglycine and its salts are conveniently applied in an aqueous formulation as a post-emergent phytotoxicant for the control of numerous plant species. N-Phosphonomethylglycine and its salts are characterized by a broad spectrum activity, i.e., they control growth of a wide variety of plants.
Commercial compositions containing N-phosphonomethylglycine are usually aqueous solutions wherein the N-phosphonomethylglycine is present as a herbicidally acceptable salt, such as the trimethyl sulfonium salt, an alkali metal salt, the ammonium salt or the salt of an amine having a molecular weight of less than about 300. The monoisopropylamine salt of N-phosphonomethylglycine is the most widely used salt in such aqueous compositions. In addition, such compositions usually contain a surfactant to enhance the effectiveness of the N-phosphonomethylglycine when it is applied to the foliage of various plants. The most widely used surfactant in commercial compositions is an ethoxylated fatty acid amine.
It is known to those skilled in the art that a particular surfactant used in an aqueous composition with a herbicide can enhance the effectiveness of the herbicide, whereas other surfactants have very little, if any beneficial effect, and in fact, some may be antagonistic. Wyrill and Burnside, Weed Science, Vol. 25 (1977), p 275-287, examined solutions containing different classes of surfactants, including polyoxyethylene stearyl methyl ammonium chlorides containing respectively 2 and 15 oxyethylene units. Some classes of surfactant were more effective than others in enhancing the herbicidal effect of N-phosphonomethylglycine (used as a solution of the isopropylamine salt), and Wyrill and Burnside concluded that an effective surfactant is a critical component of any aqueous composition containing N-phosphonomethylglycine.
Although certain surfactants may enhance the biological activity of N-phosphonomethylglycine, many of such surfactants are difficult to incorporate into aqueous compositions containing N-phosphonomethylglycine because of the pH and the ionic strength of the aqueous composition, and other factors that effect viscosity, haziness and other physical characteristics that are desired by the end user. In addition, even though N-phosphonomethylglycine is known to be relatively non-toxic and environmentally acceptable, the surfactant in some situations can be toxic to aquatic life, and/or cause skin irritation or eye irritation when in contact with the skin or the eye.
Accordingly, it would be desirable to obtain an aqueous composition containing N-phosphonomethylglycine which employs a surfactant that enhances the biological effect of N-phosphonomethylglycine but would have lower irritation and toxicity than other surfactants. It has been found that certain quaternary ammonium compounds disclosed in U.S. Pat. No. 3,619,351 are effective in enhancing the herbicidal activity of N-phosphonomethylglycine, and that aqueous compositions containing such quaternary ammonium compounds are virtually non-toxic and non-irritating to the skin and eye. However, such aqueous compositions containing the quaternary ammonium compounds are often hazy, indicating that the surfactant is only partially in solution, and will result in phase separation over time and require agitation before use. The phase separation will decrease the biological effectiveness of the formulation, as well as being aesthetically undesirable to the end user.
Now it has been found that an aqueous composition can be prepared which incorporates all the desired properties of enhancing the biological activity of N-phosphonomethylglycine, is virtually non-toxic and non-irritating to the skin and eye, and which is not hazy, but rather is a clear solution.